Java native methods, somebody please help

Can somebody tell me how I can map a C structure to a Java object? What happens when there are pointers in the C structure. How do I map those? I keep digging on the net but keep on finding those useless HelloWorld JNI examples. Is there any hopes to find a decent real world example of how to map legacy C code to java. I wanna create a JNI binding to the a C library which is heavy with structures. I need to know how to map a Java class to a C structure. Thanks, Frank